With regard to sliding structural members used for a power plant and a power transmission device, etc., a research is energetically developed to reduce friction for the purpose of the protection of the global environment. Such a research is directed to a protection of sliding members which slide against each other and improvement of fuel efficiency, and various schemes have been proposed.
As for the above mentioned directions, a scheme is proposed which allows an amorphous hard carbon film (also referred to as a diamond-like carbon film (DLC film)), graphite (graphite) and molybdenum disulfide (MoS2) to coexist. Here, MoS2 is known as a material having a layered crystal structure and as a material which can accomplish an excellent lubrication effect since it slides in a certain direction when a heavy load is applied.
As an example of such a scheme, Patent Document 1 discloses the use of an amorphous hard carbon film (described as an amorphous carbon coated film in Patent Document 1). Herein, the amorphous hard carbon film has the ratio (strength ratio) between an amorphous structure and a graphite structure limited within a predetermined range and MoS2 of equal to or greater than a predetermined amount.
Further, with respect to other schemes, proposed are addition of a predetermined component to an amorphous hard carbon film and a lubricant so as to suppress a chemical reaction in molybdenum oxide, limitation of a counterpart member, and adoption of an additional specific system.
For example, Patent Document 2 discloses that sulfur, magnesium, titanium or calcium component is added to an amorphous hard carbon film (described as an amorphous carbon coated film in Patent Document 2). Moreover, for example, Patent Document 3 discloses that copper dithiophosphate (Cu-DTP) is added to a lubricant. Patent Document 4 discloses a limitation of a ceramic coating film applied to a counterpart member. Patent Document 5 discloses an addition of a specific cooling system.
Furthermore, as another scheme, proposed is a use of an amorphous hard carbon film having hydrogen content regulated to a low level and a lubricant.
Patent Document 6 discloses, as an example such a scheme, an amorphous hard carbon film (described as a hard carbon thin film in Patent Document 6) having hydrogen content set to be 25 mass % or less, more preferably, 5 mass % or less, and further preferably, 0.5 mass % or less, and still further preferably, containing no hydrogen.